What is Unique key and Alternate Key?

Is unique key and Alternate Key same?

Primary Key ==> Is used to uniquely identify records and doesn't allow NULL values. Unique Key ==> Is also used to uniquely identify records but does allow NULL Values per column combination. Alternate Key ==> Is another type of Unique key, which is used to identify each record uniquely. This is not a constraint.

What is an Alternate Key?

Alternate keys are those candidate keys which are not the Primary key. There can be only one Primary key for a table. Therefore all the remaining Candidate keys are known as Alternate or Secondary keys.

What is alternative key and example?

All the keys which are not primary key are called an Alternate Key. Example: In this table, StudID, Roll No, Email are qualified to become a primary key. But since StudID is the primary key, Roll No, Email becomes the alternative key.

What is the difference between key and unique key?

A primary key is a column of table which uniquely identifies each tuple (row) in that table. Primary key enforces integrity constraints to the table. ... Comparison Chart:ParameterPRIMARY KEYUNIQUE KEYNumber of keys that can be defined in the tableOnly one primary keyMore than one unique key